Field of the Invention
This is a novel process for reducing the cyclic imidic ester content of an isocyanatoalkyl ester of an organic carboxylic acid. In particular, this process relates to the use of an organic acid chloride, chloroformate, thiochloroformate, sulfonyl chloride, phosphoryl chloride or like compound to react preferentially with a cyclic imidic ester at elevated temperatures. The resulting adduct is conveniently removed by distillation.
An isocyanatoalkyl ester can be prepared according to the teachings in British Pat. No. 1,252,099 by reacting a 2-oxazoline or an oxazine in a water-immiscible solvent with phosgene in the presence of an aqueous solution of a hydrogen chloride acceptor. The crude product produced by this method contains small amounts (generally, 0.1-2.0 weight percent) of the 2-oxazoline or the oxazine starting material. The only method employed in the prior art to purify these isocyanatoalkyl esters is fractional distillation, which is effective to remove 2-oxazolines or oxazines, but is not efficient. Frequently, several sequential distillations of the isocyanatoalkyl ester must be employed, to attain product of suitable purity with good recovery. In some utilities, it is critical that the level of cyclic imidic ester impurities is less than that attainable by fractional distillation.
U.S. Pat. No. 3,326,929 teaches that acid chlorides and acid anhydrides can be employed to remove amine and hydroxyl impurities from a 2-oxazoline compound. However, nothing in this reference suggests that these agents can be employed to reduce the 2-oxazoline content of an isocyanatoalkyl ester of a carboxylic acid.